What Does Science Say About Homosexuality?

May 07, 2006|By Jack Drescher, Special to the Daily Press

In communities across America, people are confronting questions about the civil and legal rights of gay and lesbian citizens. Often these conversations are spurred by legislative efforts that would adversely affect gays and lesbians. In Virginia, for example, voters will be asked in November to say whether they want to restrictively amend the state constitution to define marriage as only a union between a man and woman.

The issues involved in these conversations are complex and emotional. Ethics and religion are often central to them, but science, too, has been drawn into these discussions. What does science have to say? What questions does it grapple with? For example:

Are people "born gay"? This question has vexed sexologists and physicians since science began studying homosexuality in the 19th century. In recent years, the question has intrigued the popular imagination: The issue of what civil rights society should accord its gay and lesbian members may hinge on the answer.

To date, science can only respond that the causes of homosexuality -- and heterosexuality for that matter -- are unknown. This may not be welcome news to a culture accustomed to distilling difficult answers into easy sound bites. It may also not be the answer sought by those who feel heterosexuality represents the natural order and that homosexuality can only be explained as sin, illness or both.

Is homosexuality "biological"? Discussions of biology figure prominently in social debates about how to react to homosexuality. These debates have little to do with science.

For most people, the meaning of homosexuality being "biological" is that it is inborn and fixed. However, physicians know that the biological is not necessarily unchangeable. Plastic surgeons routinely change people's facial appearances.

Furthermore, some learned behaviors cannot change. For example, many songbirds hear and learn their song during a brief, critical period of early development. The song is acquired through experience, but biology determines when that event must occur. Once it learns a song, the bird is unable to unlearn it or acquire another. In other words, although a bird is not born singing her song, once she learns it, she can never change it. Could the same be true of homosexuality? No one knows.

Do we know what causes homosexuality? Although we do not definitively "know" its causes, some facts can be gleaned from the literature. For example, the old psychoanalytic theory (and now popular belief) that parents are the cause has fallen into disrepute. One of the largest studies ever done (979 homosexual and 477 heterosexual men and women) asked about early family relationships and found no evidence that a particular upbringing produced homosexual children -- nor heterosexual children for that matter. And despite growing claims that people can change their homosexual orientation if they try hard enough, what little scientific literature exists on this subject indicates most people, no matter how motivated, fail to change.

These facts -- that families do not seem to cause homosexuality and that changing sexual orientation is difficult, if not impossible -- support the popular view that homosexuality is "biological" or that people are "born gay." Although no "causal" link has been found, scientific data indicate some role for biology in the development of homosexuality.

Is homosexuality genetic? There is much popular interest in the "gay gene." Despite press reports announcing its discovery, no such gene has been found. The genetics of homosexuality has been indirectly investigated using studies comparing rates of homosexuality between identical and fraternal twins.

When a single fertilized egg splits in two and each half becomes a separate embryo, twins with identical genes develop. Fraternal twins, who do not share identical genes, result when two sperm fertilize two different eggs. Fraternal twins, on average, share only half of their genes.

If homosexuality were purely genetic, identical twins would both be either gay or heterosexual 100 percent of the time. Instead, the occurrence of homosexuality in both identical twins was 52 percent -- significantly higher than the 22 percent rate found in fraternal twins. The rate for nontwin biological brothers was 9 percent.

Assuming that environmental influences are the same for brothers reared together, the higher rate in identical twins suggests a strong genetic effect. However, since the rate is not 100 percent, many scientists believe there are environmental components as well. As yet, no one has separated out genetic and environmental factors from each other.